1. Field of the Invention
The present invention relates to depth gauges for biopsy needles or other medical needles and in one embodiment of the invention, to such a needle depth gauge incorporating a tip guard adapted to cover the sharp point of the needle when it is not in use.
2. Description of Related Art
Needles are commonly employed to obtain biopsy specimens for laboratory evaluation. This entails a surgical procedure which requires that the surgeon know precisely the depth to which the needle is inserted in the patient's tissue to be sure that a proper specimen is obtained. Typically, spaced markings are provided along the surface of the needle to indicate the depth of penetration of its tip. A depth stop may be employed to limit penetration of the needle to the desired depth.
U.S. Pat. No. 3,477,437, issued Nov. 11, 1969 to A. M. Goldberg, discloses a depth stop comprising an open-wound metal coil spring which grips the smooth outer surface of a hypodermic needle to be used in performing a thoracentesis procedure. The surgeon first inserts the needle to the proper depth, then places the coil spring on the needle shaft by wedging the latter between adjacent coils of spring, so that the spring extends laterally from the needle to form a stop which will ensure that the needle will not inadvertently be inserted to a greater depth during the procedure. The Goldberg coil spring may be adjusted along the length of the needle shaft after it is first wedged in place, but such adjustment is awkward because the spring is not easily unsprung to decrease the friction between needle and spring.
U.S. Pat. No. 1,436,707, issued Nov. 28, 1922 to G. Gaschke, also discloses a stop guard for hypodermic needles, which in this instance comprises a length of spring steel bent into a V-shape and formed with a pair of aligned perforations through which the needle shaft is passed. Tension on the needle shaft from the spring metal holds the guard in place. When adjustment is required, the user may squeeze the ends of the spring steel together, thus releasing the frictional hold on the needle shaft, and then slide the stop along the needle shaft to the appropriate position. Because the spring metal engages the needle in a limited contact area, a large spring force is required to provide a frictional force great enough to hold the stop from sliding. The high spring force, on the other hand, makes unspringing the device difficult. It is also to be noted that the Gaschke stop guard does not provide any protection against the needle's sharp point when the needle is not in use.
U.S. Pat. No. 4,022,191, issued May 10, 1977 to K. Jamshidi, discloses a coaxial biopsy needle guard and depth stop. More particularly, a tubular sleeve guard is attached to the hub of a syringe and fits over the needle, so that the entire needle is enclosed within the sleeve guard. The guard is formed with a series of circumferential grooves spaced along its length so that a preselected longitudinal portion of the guard may be broken off. The portion remaining provides a depth stop to limit travel of the needle into the body. The Jamshidi guard permits only a limited number of preset depths, and is nonfunctional as a needle guard once a portion is broken off to form a depth stop.
U.S. Pat. No. 5,067,946, issued Nov. 26, 1991 to S. Zhadanov, discloses a needle guard formed as an inner tube which fits over and holds the shaft of a needle, and an outer tube adjustable along the shaft of the needle by means of a pinionlike finger wheel having teeth which engage racklike teeth on the inner tube. When pressure on the wheel is released, it locks in the rotational position in which it is disposed at the time, and the interengaged teeth thereby prevent movement of the outer tube relative to the needle shaft. The outer tube thus comprises an adjustable protective tube having a limited range of motion, which may be easily moved to cover or uncover the needle's sharp point. The design is relatively complex, requiring two coaxial tubes to cover the needle, and a toothed wheel carried by the outer tube. Further, the protective cover may be adjusted over only a small distance because the wheel cooperates with a limited number of teeth formed on the first tube. It is also pointed out that nothing in the disclosure of the Zhadanov patent implies that the device might function as a depth stop.